In my U.S. Pat. No. 4,069,460, which issued Jan. 17, 1978, to the assignee of the present invention, a current comparator is disclosed. This comparator has an output equal to the difference between the two currents flowing in the input nodes. The comparator was described as having very high sensitivity in that differential currents of 0.01% could be detected. Thus, the circuit has a vanishingly small deadband range. Deadband would be defined as the range of differential current values for which there would be no output. Thus, in patent 4,069,460, with one milliampere currents being compared, a current difference of only 10 picoamperes would be detected.
Current comparators have proven to be useful in monolithic integrated circuit (IC) designs. However, there are situations where it would be desirable to have a comparator with a relatively large controlled deadband. For example, in AM radio stereo systems phase detectors may be employed to decode one of the stereo channels. Such systems are often subject to spurious responses that make stereo reception difficult. Typically, such spurious responses mistune the phase detectors. If a current comparator is coupled to sense the currents in the phase detector and its deadband adjusted to accommodate a normal tuning range, excess phase can be sensed at the output of the comparator. When such a condition is sensed, the system can be switched to nonaural or an indicator operated to show mistuning.